(19)
(11) EP 1 942 518 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
20.04.2011 Bulletin 2011/16

(43) Date of publication A2:
09.07.2008 Bulletin 2008/28

(21) Application number: 08250017.4

(22) Date of filing: 03.01.2008
(51) International Patent Classification (IPC): 
H01J 49/02(2006.01)
H03F 1/34(2006.01)
 G01R 19/00(2006.01)
(84) Designated Contracting States:
AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MT NL NO PL PT RO SE SI SK TR
Designated Extension States:
AL BA MK RS

(30) Priority: 03.01.2007 US 878299 P
20.12.2007 US 961539

(71) Applicant: LECO CORPORATION
St. Joseph, Michigan 49085-2396 (US)

(72) Inventor:
  • Casper, Ted J.
    West Bend, Wisconsin 53095 (US)

(74) Representative: Miller, James Lionel Woolverton et al
Kilburn & Strode LLP 20 Red Lion Street
London WC1R 4PJ
London WC1R 4PJ (GB)

   


(54) Base line restoration circuit


(57) Circuit for correcting base line shift of the detector coupling circuit of a TOFMS provide gain and impedance characteristics that compensate for the AC coupling effect of the detector. In one circuit (20), base line correction is achieved by injecting a current equal to that which flows due to the buildup charge in the detectors AC coupling network. In another circuit, the current source drives an integrator which is coupled to the signal path to reduce the detector AC coupling effects. In another circuit, a low noise amplifier utilizes a feedback network that reduces the detector AC coupling effects. In yet another circuit, an operational amplifier is employed to reduce the detector AC coupling effects.







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